Village Sanitary Emwmy. 
237 
4. — SJcefch of Tayhine and 
Duuhlc act 'nvj Punqj. 
The turbine, on tlie contrary, moves rapidly, and a double-acting' 
lift and force-pump can be associated with it with advantage. 
Where the stream has a fall of less than 3 or 4 feet, and par- 
ticularly if great variations take place in the quantity of water 
constituting the motive-power, it will be found that the Poncelet 
undershot, or the breast-wheel will give the best result, which, 
having regard to the loss due to pumps and gearing, practically 
amounts to 35 per cent., or about one-third of the whole theo- 
retical power due to the fall driving the wheel : thus, 
'Tails, fallino; per miuute X height of full . , . , 
\ X ' ,^ = gallons raised per imuute. 
•' elevation required 
For instance, an undershot wheel working with a fall of 3 feet 
will raise 10,000 gallons daily to a height of 100 feet, and a 
distance of one mile, with a flow 
of 945 gallons per minute. When Fi 
the fall exceeds 4 feet the overshot 
wheel or the turbine may be used, 
but the latter is generally the 
cheaper of the two ; and, as it occu- 
pies the least space and will work 
below water, it has advantages su- 
perior to the water-wheel. The 
turbine was brought very closely to 
its present perfection by M. Foui- 
neyron, whose machines have not 
been superseded, although many 
attempts have been made to do 
so. There is, however, no ma- i= 
chine which requires more ab- Tniinc j= 
solute perfection in its proportions iu^— ' 
to give a good result than the tur- 
bine, and many that are sold are very far from being fully effective, 
from imperfect design or construction. On a large scale, very 
high results have been obtained ; but for small applications, such 
as those of water-supply to villages, 70 per cent, of the power ex- 
pended may be considered the limit of perfection, and from this 
must be deducted the further loss due to the pump and gearing, 
which will reduce the product to 50 per cent. To ascertain the 
quantity of water raised per minute, by a given fall and quantity, 
the following rule may be used for turlnnes : — 
gallons falling per minute x heioilit of fall _ 
nising .1 
sucTionpiP^ 
galls, raised per minute. 
= gallons falling per minute, 
height of fall. 
For instance, with a fall of 20 feet a turbine will raise 10,000 
2 X elevation required. 
X gallons to be raised x height to be raisi 
